U.S. patent application number 13/236352 was filed with the patent office on 2012-11-22 for brushless alternator.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Hideyuki Hayashi, Yasuhiko Sugitani, Tomoki Takahashi.
Application Number | 20120293039 13/236352 |
Document ID | / |
Family ID | 47155821 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120293039 |
Kind Code |
A1 |
Hayashi; Hideyuki ; et
al. |
November 22, 2012 |
BRUSHLESS ALTERNATOR
Abstract
A brushless alternator of the present invention includes: a yoke
whose inner circumferential surface is radially opposite via an air
gap to a rotor revolvably supported by brackets; a stat or
supported by the brackets, for forming a magnetic circuit along
with the rotor and the yoke; a bobbin for engaging with the outer
circumferential surface of a thin portion of the yoke; a field coil
wound around the bobbin, for producing magnetic flux; and a plate
joined to the thin portion, for axially holding the bobbin; wherein
the thin portion of the yoke and the other portion thereof are
integrally formed in one piece using a single member.
Inventors: |
Hayashi; Hideyuki;
(Chiyoda-ku, JP) ; Sugitani; Yasuhiko; (Bunkyo-ku,
JP) ; Takahashi; Tomoki; (Chiyoda-ku, JP) |
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Tokyo
JP
|
Family ID: |
47155821 |
Appl. No.: |
13/236352 |
Filed: |
September 19, 2011 |
Current U.S.
Class: |
310/263 |
Current CPC
Class: |
H02K 3/46 20130101; H02K
19/24 20130101 |
Class at
Publication: |
310/263 |
International
Class: |
H02K 1/22 20060101
H02K001/22 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2011 |
JP |
2011-113608 |
Claims
1. A brushless alternator, comprising: a shaft; a rotor having a
magnetic pole, for revolving along with the shaft; a stator
disposed outside the rotor opposite thereto; a bracket for
revolvably supporting the shaft and housing therein the rotor and
the stator; a yoke fixed to the bracket, whose inner
circumferential surface is opposite to the rotor via an air gap,
for forming a magnetic circuit along with the rotor and the stator;
a bobbin for engaging with the outer circumferential surface of a
thin portion of the yoke whose outer diameter is smaller than that
of the other portion of the yoke; a field coil wound around the
bobbin, for producing magnetic flux; and a holding member joined to
the thin portion, for axially holding the bobbin; wherein the thin
portion of the yoke and the other portion thereof are integrally
formed in one piece using a single member.
2. A brushless alternator according to claim 1, wherein the holding
member is joined to an axial end face of the thin portion and the
width of the air gap at the thin portion of the yoke is the same as
that at the other portion thereof.
3. A brushless alternator according to claim 1, wherein the axial
length of the bobbin and that of the thin portion are substantially
the same.
4. A brushless alternator according to claim 1, wherein an axial
end face of the bobbin abuts the holding member all over the
face.
5. A brushless alternator according to claim 1, wherein the thin
portion and the holding member are joined together by
resistance-welding.
6. A brushless alternator according to claim 5, wherein the
brushless alternator is a vehicle-use brushless alternator.
7. A brushless alternator according to claim 1, wherein the bracket
and the yoke are fixed to each other by riveting.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the invention
[0002] The present invention relates to brushless alternators.
[0003] 2. Description of the related art
[0004] The rotor of an alternator used for a vehicular AC generator
is revolved by a vehicle engine by way of a shaft, a pulley and a
belt. The alternator has been increasing in size and weight as an
electrical load of the vehicle becoming heavier; therefore, the
increase in weight of the rotor itself now imposes a heavy burden
on the engine. In particular, the increase in the rotor weight and
inertia results in shortage of engine drive torque, causing a
serious problem in the light of reducing idle revolution speed and
enhancing acceleration capability. In order to decrease the weight
and inertia of this rotor and furthermore to cope with increasing
demand for enhanced longevity in recent years, a brushless
alternator has been conventionally known, in which the field coil
of the rotor is fixed to a bracket, and a claw-shaped magnet pole
portion for conducting magnet flux revolves (refer to Patent
Document 1, for example).
[0005] The brushless alternator shown in Patent Document 1 includes
a bobbin on which the field coil is fixed, and a step portion
provided on a second ring-shaped yoke constituting the bobbin is
fixed to one end of a cylindrical portion of a plate for
restricting axial movement of the bobbin. There is proposed a
structure in which the radial thickness of the cylindrical portion
of the plate fixed as above is optimized, whereby its magnetic
circuit can be improved and output from the brushless alternator
can be enhanced.
[0006] Patent Document 1: Japanese Laid-Open Patent Publication No.
2007-37233
[0007] In the brushless alternator described in Patent Document 1,
two factors, that is, an advantage of enhancing an output current
and output efficiency of the brushless alternator by reducing
magnetic resistance by varying the radial thickness of the
cylindrical portion of the plate and a disadvantage of the output
current and output efficiency of the alternator reducing attributed
to a decrease in a field current through the field coil, have been
taken into consideration in a comprehensive manner, and as a
result, the radial thickness of the cylindrical portion of the
plate has been quantitatively determined. However, since the
structure has a joint in the magnetic circuit, at which the step
portion of the second yoke is joined to the plate by spot-welding,
the magnetic resistance remains high at the joint due to stress
concentration attributed to the spot-welding; therefore, magnetic
flux produced by the field current in some cases is not effectively
utilized, which has resultantly caused a decrease in the output
current and output efficiency of the brushless alternator.
[0008] In the brushless alternator described in Patent Document 1
here, methods other than spot-welding, such as gluing and screwing,
are also described as a method of fixing the foregoing step portion
of the second yoke and the plate with each other; however in a
structure of using those methods, for example, the weight of the
plate itself as well as that of the bobbin including the field coil
must be supported at the joint at which the step portion of the
second yoke and the plate are joined together; therefore, there
have been disadvantages such as applications of the brushless
alternator are restricted to those used in an environment requiring
not so strict heat and vibration resistance.
SUMMARY OF THE INVENTION
[0009] The present invention has been made to resolve the problems
described above, and aims at providing a brushless alternator
capable of achieving higher output power and greater efficiency by
reducing the magnetic resistance of the magnetic circuit.
[0010] A brushless alternator according to the present invention
comprises: a shaft; a rotor having a magnetic pole, for revolving
along with the shaft; a stator disposed outside the rotor opposite
thereto; a bracket for revolvably supporting the shaft and housing
therein the rotor and the stator; a yoke fixed to the bracket,
whose inner circumferential surface is opposite to the rotor via an
air gap, for forming a magnetic circuit along with the rotor and
the stator; a bobbin for engaging with the outer circumferential
surface of a thin portion of the yoke whose outer diameter is
smaller than that of the other portion thereof; a field coil wound
around the bobbin, for producing magnetic flux; and a holding
member joined to the thin portion, for axially holding the bobbin;
wherein the thin portion of the yoke and the other portion thereof
are integrally formed in one piece using a single member.
[0011] According to a brushless alternator of the present
invention, the joint between the yoke constituting part of the
magnetic circuit for the magnetic flux produced by the field coil
and the holding member for axially fixing the bobbin around which
the field coil is wound is located at a point distant from the
magnetic circuit, so that the magnetic resistance of the circuit
can be reduced. Therefore, a brushless alternator enhancing the
output power and efficiency thereof can be provided.
[0012] The foregoing and other object, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an enlarged axial cross-sectional view of the
essential portion of a brushless alternator according to Embodiment
1 of the present invention;
[0014] FIG. 2 is a perspective view of a second yoke of the
brushless alternator shown in FIG. 1; and
[0015] FIG. 3 is an axial cross-sectional view of the brushless
alternator shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0016] FIG. 1 is an enlarged axial cross-sectional view of the
essential portion of a brushless alternator according to Embodiment
1 of the present invention; FIG. 2, a perspective view of a second
yoke of the brushless alternator shown in FIG. 1; and FIG. 3, an
axial cross-sectional view of the brushless alternator shown in
FIG. 1.
[0017] Firstly, the structure of the brushless alternator according
to Embodiment 1 of the present invention will be explained.
[0018] In FIG. 3, the brushless alternator 1 comprises: a front
bracket 20 and a rear bracket 21 integrated with each other by a
through bolt 23; a stator 14 fixed to the front bracket 20 and the
rear bracket 21, including a stator core 15 and a stator winding 16
wound around the stator core 15; a shaft 17 both ends of which are
revolvably supported by a front bearing 18 and a rear bearing 19
fitted to the front bracket 20 and the rear bracket 21,
respectively; a rotor 2 fixed to the shaft disposed inside the
stator 14; a rectifier 22 electrically connected to the stator
winding 16, for converting AC into DC output; and a regulator (not
shown in the figure) electrically connected to the rotor 2, for
regulating within a predetermined range an AC voltage generated by
the stator winding 16.
[0019] The shaft 17 extends outwardly of the front bracket 20 side;
a pulley 24 is fixed to this extending portion. This pulley 24 and
the engine (not shown in the figure) are bound together with a belt
so that the shaft 17 is set to revolve driven by the engine by way
of the belt.
[0020] And, the front bracket 20 revolvably supports one end of the
shaft 17 by way of the front bearing 18; the rear bracket 21
revolvably supports the other end thereof by way of the rear
bearing 19. The rotor 2 is thereby revolvably disposed inside the
front bracket 20 and the rear bracket 21.
[0021] The rotor 2 includes a magnetic pole core 3 and a field coil
13 disposed inside this magnetic pole core 3.
[0022] The magnetic pole core 3 includes a front magnetic pole core
4 disposed in the front bracket 20 side and a rear magnetic pole
core 8 disposed in the rear bracket 21 side.
[0023] The front magnetic pole core 4 includes a first cylindrical
boss portion 5 fixed to the shaft 17 with the shaft inserted
therethrough at the center; a first thick ring-shaped yoke 6
extending radially and outwardly from one end of the first boss
portion 5; and a first claw-shaped magnetic pole portion 7 whose
tip portion extends toward the rear bracket 21 side, along the
shaft axis, from the outer circumferential surface of the first
yoke 6.
[0024] The rear magnetic pole core 8 includes a second cylindrical
boss portion 9 fixed to the shaft 17 with the shaft inserted
therethrough at the center; a second yoke 10 disposed radially
outside the second cylindrical boss portion 9 via a narrow air gap;
and a second claw-shaped magnetic pole portion 11 disposed radially
outside the second yoke 10 via another narrow gap and whose tip
portion extends toward the front bracket 20 side along the shaft
axis.
[0025] Opposing axial end faces of the second boss portion 9 and
the first boss portion 5 are in surface contact with each other.
The second claw-shaped magnetic pole portion 11 and the first
claw-shaped magnetic pole portion 7 are disposed so that their tip
portions engage with each other. Inner circumferential surfaces of
the first claw-shaped magnetic pole portion 7 and the second
claw-shaped magnetic pole portion 11 each are joined to the outer
circumferential surface of an annular ring 12 made of non-magnetic
material, all over the circumferential surface thereof, by welding
or hard soldering; therefore the first claw-shaped magnetic pole
portion 7 and the second claw-shaped magnetic pole portion 11 are
joined together by way of the ring 12.
[0026] The field coil 13 is disposed in a space created by the
first claw-shaped magnetic pole portion 7 and the second
claw-shaped magnetic pole portion 11 opposite to this first
claw-shaped magnetic pole portion 7.
[0027] The field coil 13 is wound from a wire around the bobbin 32
made of nylon resin, sharing a common axis with the shaft 17. The
lead wires (not shown in the figure) at both ends of the wire wound
a plurality of turns around the bobbin 32 are connected to the
regulator. The bobbin includes a cylindrical portion 320 and a pair
of flanges, a first flange 321 and a second flange 322, that extend
radially and outwardly from the respective ends of the cylindrical
portion 320.
[0028] As shown in FIG. 1, the second yoke 10 includes a
cylindrical thin portion 101 and a cylindrical thick portion 100
that extends axially from one end of the thin portion 101 and whose
outer diameter is larger than that of the thin portion 101, and
those are integrally formed in one piece using a single member.
Moreover, the inner diameter of the thick portion 100 is equal to
that of the thin portion 101, forming the same inner circumference
surface.
[0029] The inner circumferential surface of the thick portion 100
is opposed to the outer circumferential surface of the second boss
portion 9 via the narrow air gap, and that of the thin portion 101
to the outer circumferential surface of the first boss portion 5
also via a narrow air gap.
[0030] The inner circumferential surface of the cylindrical portion
320 of the bobbin 32, which constitutes the field coil 13, engages
with the outer circumferential surface of this thin portion 101;
the first flange 321 of the bobbin 32 abuts an axial end face of
the thick portion 100. A discoid plate 31 made by pressing soft
steel sheet, which serves as a holding member for restricting axial
movement of the bobbin 32, is joined to an axial end face of the
thin portion 101 of the second yoke 10, and also abuts an axial end
face of the second flange 322 of the bobbin 32. The bobbin 32 is
thereby held on the second yoke 10. In addition, the second yoke 10
is fixed to the rear bracket 21.
[0031] As to each of dimensional relations among the second yoke
10, the bobbin 32 and the plate 31, the inner diameter of the
cylindrical portion 320 of the bobbin 32 is substantially the same
as the outer diameter of the thin portion 101 of the second yoke
10; the axial length of the bobbin 32 is substantially the same as
that of the thin portion 101 of the second yoke 10. Furthermore,
the radial length of each of the first flange 321 and the second
flange 322 of the bobbin 32 is substantially the same as the radial
length of the plate 31 and that of the thick portion 100 of the
second yoke 10.
[0032] The stator 14 is disposed surrounding the outer
circumferential surface of the rotor 2. Moreover, the stator 14 is
sandwiched between the front bracket 20 and the rear bracket 21
with both axial ends of the stator core 15 held by the through bolt
23.
[0033] Next, a process of assembling the field coil 13 and the
plate 31 onto the second yoke 10 will be explained.
[0034] Firstly, the bobbin 32 is inserted onto the thin portion 101
of the second yoke 10; the first flange 321 of the bobbin 32 is
abutted with an axial end face of the thick portion 100 of the
second yoke 10. Next, the plate 31 is joined to the axial end face
of the thin portion 101 of the yoke 10 by spot-welding regularly
and sequentially at a plurality of points on the circumference.
Following that, a wire is wound around the bobbin 32 to make up the
coil 13. Lastly, the second yoke 10 is screwed in this state onto
the rear bracket 21 using fixing screws (not shown in the
figure).
[0035] In the brushless alternator 1 structured as described above,
the field coil 13 is supplied with a current from a battery (not
shown in the figure) so as to produce magnetic flux.
[0036] As shown in FIG. 1, this magnetic flux .PHI. flows through a
path in such a way that the flux transmits from the second yoke 10
to the second boss portion 9 via the narrow air gap provided
radially in the inner side of the yoke, then passes through the
first boss portion 5 that abuts the second boss portion 9 on the
inner end face thereof, the first yoke 6 and the first claw-shaped
magnetic pole portion 7, crosses the stator 14 disposed in the
radial outer side of the rotor 2, following that, the flux .PHI.
passes through the second claw-shaped magnetic pole portion 11 and
a narrow air gap provided in the radial inner side thereof, and
finally returns to the second yoke 10. Therefore, the first
claw-shaped magnetic pole portion 7 and the second claw-shaped
magnetic pole portion 11 are magnetized in the N and S poles,
respectively.
[0037] Meanwhile, the pulley 24 is driven by the engine so that the
shaft 17 to which the pulley is directly joined revolves, thereby
revolving the rotor 2. Thereby, the magnetic field produced by the
field coil 13 also revolves. The magnetic flux .PHI. constituting
this revolving magnetic field is transmitted to the stator core 15
through the foregoing path, which generates electromotive force in
the stator winding 16. This generated AC power is rectified into DC
power by the rectifier 22 and stored in the battery.
[0038] At this moment, since the field coil 13 is mounted on the
second yoke 10 screwed onto the rear bracket 21, the coil does not
revolve, but the front magnetic pole core 4 that is integrally
formed of the first boss portion 5, the first yoke 6 and the first
claw-shaped magnetic pole portion 7, the second boss portion 9 of
the rear magnetic pole core 8 and the second claw-shaped magnetic
pole portion 11 thereof revolve.
[0039] In the brushless alternator 1 according to this Embodiment 1
described above, the thin portion 101 and the thick portion 100 of
the second yoke 10 are integrally formed in one piece using a
single member, and this thin portion 101 and the plate 31 are
joined to each other at a point close to an axial end face of the
second flange 322 of the bobbin 32; therefore there is no joint
between the second yoke 10 and the plate 31 in the magnetic path
through which the magnetic flux .PHI. transmits from the second
yoke 10 to the second boss portion 9 via the narrow air gap
provided in the radial inner side thereof, whereby the magnetic
resistance of the path can be reduced, so that the magnetic
property can be enhanced. As a result, an output current from the
brushless alternator of this invention can be increased compare to
that from a conventional one in which the joint between the second
yoke and the plate exists on the magnetic path; therefore a
brushless alternator capable of achieving higher output and greater
efficiency can be provided.
[0040] Moreover, in a structure as described in this Embodiment 1,
the radial thickness t of the thin portion 101 of the second yoke
10 shown in FIG. 1 can be set in a more flexible manner. Increasing
the radial thickness t of the thin portion 101 enables a larger
contact area to be secured in joining the plate 31 to the thin
portion 101, enhancing joining workability, so that productivity of
the brushless alternator can be enhanced. However on the other
hand, the inner diameter of the field coil 31 and the coil length
become larger, and as a result, the field current flowing through
the field coil is decreased and output efficiency is lowered,
furthermore leading to an increase in the size of the brushless
alternator 1. To that end, the radial thickness t of the
cylindrical portion 101 of the second yoke 10 can be set to an
optimum value, taking into consideration in a comprehensive manner
the productivity, output power and efficiency of the brushless
alternator 1.
[0041] Furthermore, the inner diameters of the thick portion 100
and the thin portion 101 of the second yoke 10 are the same, so
that the same inner circumferential surface is formed, and the
plate 31 is joined to the second yoke 10 on the axial end surface
of the thin portion 101 of the yoke; therefore, the width of the
narrow air gap provided radially in the inner side of thick portion
100 of the second yoke 10 can be set the same as that provided
radially in the inner side of thin portion 101 of the second yoke
10. In the conventional brushless alternator, when the plate is
welded to the second yoke, weld marks stick out radially toward the
inner side thereof; therefore a structure securing a wider air gap
needs to be employed, which has been a factor of increasing the
magnetic resistance.
[0042] In this Embodiment 1, the narrow air gap provided from the
thin portion 101 radially in the inner side thereof is not
unnecessarily increased, so that the increase in the magnetic
resistance at this air gap can be suppressed. Therefore, the output
current can be enhanced compared to the conventional brushless
alternator, and as a result, a brushless alternator capable of
achieving higher output and greater efficiency can be provided.
[0043] Moreover, the brushless alternator of this Embodiment 1 is
structured in such a way that the axial length of the bobbin 32 and
that of the thin portion 101 of the yoke 10 are set substantially
the same so that a maximum area of the inner circumferential
surface of the cylindrical portion 320 of the bobbin 32 engaging
with the outer circumferential surface of the thin portion 101 of
the second yoke 10 can be secured. Therefore, heat generated in the
field coil 13 is dissipated from the thin portion 101 of the second
yoke 10 to the rear bracket 21 by way of the thick portion 100 of
the second yoke 10. In this Embodiment 1, the heat generated in the
field coil 13 is directly transmitted to the second yoke 10, there
is no joint such as a welding point in the heat dissipation path,
and the second yoke is made of a single member; therefore, heat
conductivity and heat dissipation can be enhanced compared to the
conventional brushless alternator, thereby suppressing heat
generation in the field coil 13, and as a result, a decrease in the
field current is suppressed, which can further enhance output power
and efficiency of the brushless alternator. In addition, since the
heat generation in the field coil 13 is suppressed, a brushless
alternator that excels in heat resistance and longevity can be
provided.
[0044] Furthermore, since the outer diameter of the plate 31 is
substantially the same as that of the second flange 322 of the
bobbin 32 in this Embodiment 1, the plate 31 abuts the second
flange 322 of the bobbin 32 all over the surface thereof, whereby
bearing can be reduced, so that a brushless alternator that excels
in durability can be provided.
[0045] In this Embodiment 1, since the plate 31 is joined to the
axial end face of the thin portion 101 of the second yoke 10 by
spot-welding, that is, resistance-welding, which excels in heat
resistance and enables reduction in production manpower compared to
that using soft soldering, for example, a brushless alternator can
be provided in which greater longevity and cost down through
enhanced productivity can be achieved.
[0046] Moreover, since the axial length of the bobbin 32 and that
of the thin portion 101 of the second yoke 10 are substantially the
same, even if the plate 31 is spot-welded to the axial end face of
the thin portion 101, the spot-welded points are distant from the
magnetic circuit; therefore their adverse affect on the magnetic
property will be small.
[0047] Furthermore, the brushless alternator in this Embodiment 1
is structured in such a way that the axial length of the bobbin 32
and that of the thin portion 101 of the second yoke 10 are set
substantially the same as described; therefore, the plate 31 can be
welded from the axial direction, so that the plate 31 can be easily
assembled. Furthermore, since the plate 31 can be welded to the
axial end face of the thin portion 101, a space for welding work
can be secured enough, thereby enhancing productivity. Furthermore,
dimensions of portions of the second yoke 10, the field coil 13 and
the plate 31 need to be controlled in order to firmly fix the
bobbin 32 without play in the axial direction when assembled to the
second yoke 10; however in a structure as in this Embodiment 1, the
number of such dimensions can be reduced to two including the axial
length of the thin portion 101 of the second yoke 10 and that of
the bobbin 32. In the conventional structure, dimensions of three
portions, that is, the axial length of each of the step portion of
the second yoke, the cylindrical portion of the plate and the
bobbin, need to be controlled. By structuring as this Embodiment 1,
a brushless alternator capable of achieving further enhanced
productivity and cost down can be provided.
[0048] Moreover, since the thin portion 101 and the plate 31 are
joined to each other by spot-welding that excels in heat resistance
and can secure strength, a brushless alternator according to this
Embodiment 1 can be used as a vehicular AC generator subject to a
severe environment of use such as severe temperature and
vibration.
[0049] In this Embodiment 1, a case in which the thin portion 101
is joined to the plate 31 by spot-welding has been explained;
however the welding method is not limited to this, but other
welding such as projection-welding can be used, or the plate 31 may
be press-fitted onto protrusions provided on the axial end face of
the thin portion 101. Moreover, by structuring as described above,
the plate 31 can be made smaller compared to a conventional annular
cylindrical plate having a flange extending radially; therefore
strength of the joint between the thin portion 101 and the plate 31
that sustains the plate's own weight can be reduced. Therefore, if
the joint is strong enough even by hard or soft soldering, those
soldering methods can also be used.
[0050] Moreover, welding locations of the plate 31 have been
explained to be on the axial end face of the thin portion 101 of
the second yoke 10; however the locations are not limited to this.
For example, when the plate 31 is cylindrical having a flange
extending radially, the outer circumferential surface of the
cylindrical portion may be joined to the inner circumferential
surface of the thin portion 101 by welding with the flange abutting
the axial end face of the thin portion 101.
[0051] In this Embodiment 1, the surface of the second flange 322
of the bobbin 32 abuts the plate 31 all over the surface; however
the way of abutment is not limited to this. For example, even if
the outer diameter of the plate 31 is smaller than that of the
second flange 322 of the bobbin 32, its axial movement can be
restricted as far as the plate 31 abuts at least part of the second
flange 322 of the bobbin 32.
[0052] In addition, the bobbin 20 is made of nylon resin in this
Embodiment 1; however it maybe made of thermosetting resin such as
phenol resin. Furthermore, the bobbin may be made by applying
isolating resin, that is, isolating material, between the field
coil 13 and both the thick portion 100 and thin portion 101 of the
second yoke 10 and between the field coil 13 and the plate 31, that
is, on the surfaces of the field coil except for those opposed to
the first claw-shaped magnetic pole portion 7 and the second
claw-shaped magnetic pole portion 11, or it may be made using
isolating paper.
[0053] Moreover, the second yoke 10 engaging with the field coil 13
is disposed as screwed to the rear bracket 21 side in this
Embodiment 1; however it can be disposed in the front bracket 20
side. In order to do that, locations of the magnetic pole core 4
and the magnetic pole core 8 may be exchanged between them.
[0054] Furthermore, the second yoke 10 is fixed to the rear bracket
21 using a fixing bolt; however it can be fixed using glue or by
riveting or the like. Fixing by riveting would suppress the second
core coming off better than fixing with the fixing bolt or
glue.
[0055] Various modifications and alterations of this invention will
be apparent to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this is not limited to the illustrative embodiments set forth
herein.
* * * * *